chore(deps): Bump native-buildtools.version from 0.9.18 to 0.9.20

Bumps `native-buildtools.version` from 0.9.18 to 0.9.20.

Updates `junit-platform-native` from 0.9.18 to 0.9.20
- [Release notes](https://github.com/graalvm/native-build-tools/releases)
- [Commits](https://github.com/graalvm/native-build-tools/commits)

Updates `native-maven-plugin` from 0.9.18 to 0.9.20
- [Release notes](https://github.com/graalvm/native-build-tools/releases)
- [Commits](https://github.com/graalvm/native-build-tools/commits)

---
updated-dependencies:
- dependency-name: org.graalvm.buildtools:junit-platform-native
  dependency-type: direct:development
  update-type: version-update:semver-patch
- dependency-name: org.graalvm.buildtools:native-maven-plugin
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

Signed-off-by: dependabot[bot] <[email protected]>

pom.xml

@@ -170,7 +170,7 @@
             <id>native</id>
             <properties>
                 <repackage.classifier>exec</repackage.classifier>
-                <native-buildtools.version>0.9.18</native-buildtools.version>
+                <native-buildtools.version>0.9.20</native-buildtools.version>
             </properties>
             <dependencies>
                 <dependency>